import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

/**
 * Created with IntelliJ IDEA.
 * Description:
 * User:
 * Date: 2025-06-19
 * Time: 20:24
 */
public class UdpEchoServer {
    private DatagramSocket socket = null;

    public UdpEchoServer(int port) throws SocketException {
        socket = new DatagramSocket(port);
    }

    public void start() throws IOException {
        System.out.println("服务器启动！");
        while(true){
            //1.读取请求并分析
            DatagramPacket requestPacket = new DatagramPacket(new byte[4096], 4096);
            socket.receive(requestPacket);
            //把读取到的二进制数据，转成字符串，只构造有效部分
            String request = new String(requestPacket.getData(),0, requestPacket.getLength());
            //2.根据请求，计算响应（服务器最关键的逻辑）
            String response = process(request);
            //3.把响应返回客户端
            DatagramPacket responsePacket = new DatagramPacket(response.getBytes(), response.getBytes().length, requestPacket.getSocketAddress());
            socket.send(responsePacket);
            //4.打印日志
            System.out.printf("[%s:%d] req:%s, resp:%s\n", requestPacket.getAddress(), requestPacket.getPort(), request, response);

        }
    }

    private String process(String request) {
        return request;
    }

    public static void main(String[] args) throws IOException {
        UdpEchoServer server = new UdpEchoServer(9090);
        server.start();
    }
}
